Aluminum bar and production method thereof

ABSTRACT

A production method of an aluminum bar includes a surface pressing step of pressing a surface of an aluminum bar with pressure rollers. A pressing force of the pressure rollers in the surface processing step is set within a range of 1.5 Fc to 4.0 Fc, where, in a relationship between a pressing force of the pressure rollers to the aluminum bar and a straightness of the aluminum bar, when a boundary point at which a section where the straightness of the aluminum bar improves as the pressing force of the pressure rollers increases shifts to a section where the straightness does not change as the pressing force of the pressure rollers increases is a straightness saturation point, and the pressing force of the pressure rollers at the straightness saturation point is “Fc”.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

The present application claims priority to Japanese Patent Application No. 2014-221296 filed on Oct. 30, 2014, the entire disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Some embodiments of the present invention relate to a production method of an aluminum bar in which a bar-shaped aluminum material is pressed by pressure rollers and an aluminum bar produced by the method. In this disclosure, the term “aluminum (Al)” is used to include the meaning of aluminum alloys (Al alloys).

2. Description of the Related Art

The following description of related art sets forth the inventor's knowledge of related art and certain problems therein and should not be construed as an admission of knowledge in the prior art.

A round bar-shaped aluminum bar which is used as a forging blank is made of, for example, a continuously cast bar. In producing a continuously cast bar, as described in Patent Document 1 (Japanese Unexamined Laid-open Patent Application Publication No. 2004-314176), a consistent production line is well known, in which a continuously cast bar (bar-shaped member) obtained by casting is sequentially subjected to a cutting step, a heat treatment step (homogenization treatment step), a pre-straightening step (first straightening step), a peeling step (surface cutting step), a post-straightening step (second straightening step), and a visual inspection step, and then packed and carried out.

In the consistent production line, the aluminum bar in which the outer peripheral surface was removed in the peeling step is straightened to correct the bend using straightening rolls as described in the aforementioned Patent Document 1 or Patent Document 2 (Japanese Patent No. 5211928) in a post-straightening step to increase the inspection accuracy in the inspection step. However, in the aforementioned production line, since the bar will not be especially subjected to a surface treatment after the peeling step, damage occurred after the peeling step remain. For this reason, such damage may sometimes cause the following inconveniences.

In the meantime, in the aforementioned production line for a continuously cast bar, for example, a rolling conveyance system is used to convey the aluminum bar between steps.

FIG. 6A is a side view showing a rolling conveyance device. As shown in this figure, this rolling conveyance device is equipped with a frame 1 inclining downward toward the conveyance direction, and a plurality of round bar-shaped aluminum bars W set on the frame 1 are contiguously rolled by their self-weights and conveyed.

As shown in FIG. 6A, in such a rolling conveyance, in theory, adjacent preceding and following bars W and W are in line contact with each other along a line in the axial direction (longitudinal direction). However, in reality, as shown in FIG. 6B and FIG. 6C, they are not in line contact, but in point contact with each other at a number of points along a line in the axial direction depending on the respective bent states and/or respective surface states of the bars W.

Here, as shown in FIG. 6B and FIG. 6C, when a contact point to which the strongest force is acting among contact points of adjacent preceding and following bars W and W is referred to as “Wc”, at the contact point Wc, the front side (preceding) bar W moves upward and the rear side (following) bar W moves downward. In other words, since the front (preceding) and rear (following) bars W and W are moving in opposite directions at the contact point Wc, a force is applied to the contact point Wc in the circumferential direction. The force applied to the contact point Wc is not only affected by the weight of one rear (following) side bar W, but also is affected by the total weight of all bars W existing on the rear side with respect to the contact point Wc, so it is a considerable force. Specifically, when the total weight of bars W on the rear side with respect to the contact point Wc is “m”, the gravitational acceleration is “g”, and the force obtained when the inclination angle of the frame 1 is “θ” is “F”, there is a correlation of F=m·g·sin θ. This force F is applied to the contact point Wc.

In this way, since a large force is acting on the contact point Wc, when a surface of either one of the bars W and W positioned adjacently at a position corresponding to the contact point Wc has a protruding damage which occurred in a previous step, the protruding damage cuts into the surface of the other bar W to cause a scratch by the force in the circumferential direction, resulting in new damage on the surface of the other bar W.

FIGS. 7A and 7B shows a typical example of scratch damage. As shown in this figure, the scratch damage 2 is not a simple spot-shaped scratch, but a scratch that spreads in a wide range in a manner as to extend on the circumferential surface of the bar, starting from a portion where the scratch occurred at the contact point Wc. In detail, the damage 2 includes a concave part 21 formed by gouging a part of the surface of the bar and a convex part 22 plastically deformed by moving the gouged part of the surface of the bar. Further, for the outer diameter dimension of the damage 2, generally, the average value of the height α2 is 50 μm to 300 μm, the average value of the starting point width β2 is 100 μm to 500 μm, and the average value of the length γ2 is 20 μm to 50 μm.

Since the newly occurred damage 2 as mentioned above includes a convex part 22, the convex part 22 becomes a starting point of new damage on an adjacent bar W in contact with the bar W having the convex part 22, which causes damage 2 on another adjacent bar W in the same manner as described above. In this way, the damage 2 is sequentially and continuously transferred to another adjacent bar W. As a result, occurrence of damage 2 spread endlessly on a number of bars W arranged on the frame 1.

On the other hand, in the case of using a bar W having damage 2 on the surface as a forging blank, the damage 2 becomes a starting point to cause a breakage at the time of forging, or remains on the surface of a forging blank even after forging. Above all, in cases where damage 2 having a certain depth remains, the damage 2 may become a forging defect.

Particularly, as shown in FIG. 7, when there is damage 2 extending in the circumferential direction on the outer circumferential surface of the forging blank, it is not preferable in a forging process.

That is, in many cases, in order to improve dimensional accuracy, a surface of a forging blank is subjected to a cutting process after forging. With this cutting process, to assuredly remove the damage, the cutting allowance (depth of the cutting process) needs to be larger than the depth of the damage. However, from the viewpoint of improving the material yield, reducing the processing labor, etc., the cutting allowance is preferably as small as possible. Further, the cutting allowance differs depending on the portion of the forging blank. Further, in a portion where the required dimensional accuracy is not strict, the forged processed surface may be kept as it is without performing a cutting process when the dimensional tolerance is permitted. In this way, there exist uncut portions or almost uncut portions (hereinafter collectively referred to as “non-cut portion(s)”) in the forging blank. On the other hand, in the case of the scratch damage 2 as mentioned above, since the dimension γ2 of the damage 2 in the circumferential direction is long, there is an increased possibility that a part of the damage 2 is present in the non-cut portion. Therefore, it is not preferable since it is difficult to assuredly cut and remove the damage 2 remaining on the forging blank and there is an increased possibility that a poor appearance may occur on the final product after cutting.

Further, in the damage 2 having such a convex part 22 as described above, the convex part 22 is pressed and crushed at the time of forging and a plastically deformed part may occur in a manner as to cover the surface of the forging blank in a layer form. The covering part in such a layer form is not preferable since there is a risk that lap defects such as minute cracks may occur.

The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred described embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.

SUMMARY OF THE INVENTION

The disclosed embodiments of this disclosure have been developed in view of the above-mentioned and/or other problems in the related art. The disclosed embodiments of this disclosure can significantly improve upon existing methods and/or apparatuses.

Some embodiments of the present invention were made in view of the aforementioned problems, and aim to provide a production method of an aluminum bar capable of preventing occurrence of damage by a surface pressing process using pressure rollers, and also aim to provide an aluminum bar produced by the method.

The other purposes and advantages of some embodiments of the present invention will be made apparent from the following preferred embodiments.

To achieve the aforementioned purposes, the inventors diligently made an effort to repeatedly conduct thorough experiments and research regarding a relationship between a correction process (surface pressing process) using straightening rolls and a surface condition of an aluminum bar.

As a result, by adding specific configurations to the surface pressing process, a configuration in which occurrence of detrimental damage can be prevented and no transfer of the damage due to rolling and carrying is recognized was discovered, and the present invention was completed.

That is, some embodiments of the present invention have the following structure.

[1] A production method of an aluminum bar, comprising:

a surface pressing step of pressing a surface of an aluminum bar with pressure rollers,

wherein a pressing force of the pressure rollers in the surface processing step is set within a range of 1.5 Fc to 4.0 Fc,

where, in a relationship between a pressing force of the pressure rollers to the aluminum bar and a straightness of the aluminum bar, when a boundary point at which a section where the straightness of the aluminum bar improves as the pressing force of the pressure rollers increases shifts to a section where the straightness does not change as the pressing force of the pressure rollers increases is a straightness saturation point, and the pressing force of the pressure rollers at the straightness saturation point is “Fc”.

[2] The production method of an aluminum bar as recited in the aforementioned Item [1],

wherein a pair of straightening rolls are used as the pressure rollers, and

wherein a straightening step for straightening an aluminum bar by passing the aluminum bar between the pair of rotating straightening rolls is also used as the surface pressing step.

[3] The production method of an aluminum bar as recited in the aforementioned Item [1] or [2], further comprising a peeling step of cutting and removing an outer peripheral surface of the aluminum bar before performing the surface pressing step.

[4] The production method of an aluminum bar as recited in any one of the aforementioned Items [1] to [3], wherein the aluminum bar is an aluminum member to be used as a forging blank.

[5] An aluminum bar produced by the production method as recited in any one of the aforementioned Items [1] to [4], wherein, among two points set on a load curve showing a relationship between a cutting level and a load length for a contour curve on a surface of the aluminum bar, when two points in which an interval of the load length becomes 60% of the entire length of the load length are a pair of measuring points, a minimum value of a slope of a straight line passing the pair of measuring points is 0.5 or less.

According to the production method of an aluminum bar as recited in the aforementioned Item [1], since a surface pressing treatment is performed by setting a pressing force to the surface of the aluminum bar within a specific range, the surface of the aluminum bar becomes in a good state, and damage can be prevented from occurring on the surface, and problems such as deformation of the aluminum bar and occurrence of roll transfer marks can also be assuredly prevented.

According to the production method of an aluminum bar as recited in the aforementioned Item [2], the surface of the aluminum bar can be finished in a good state by the straightening step for straightening.

According to the production method of an aluminum bar as recited in the aforementioned Item [3], the surface of the aluminum bar can be maintained in a good state after cutting the surface of the aluminum bar.

According to the production method of an aluminum bar as recited in the aforementioned Item [4], a high quality forged product can be assuredly obtained.

According to the aluminum bar as recited in the aforementioned Item [5], the aluminum bar can have a good surface condition, and can be suitably used as a forging blank, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are shown by way of example, and not limitation, in the accompanying figures.

FIG. 1A is a plane view showing a roll straightening machine used for a production method of an aluminum bar according to an embodiment of the present invention.

FIG. 1B is a side view showing the roll straightening machine according to the embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a straightening rolling force and a surface profile, etc.

FIG. 3 is a graph showing a load curve for explaining the surface profile according to the embodiment.

FIG. 4 is a graph showing a load curve of an aluminum bar of Example 1.

FIG. 5 is a graph showing a load curve of an aluminum bar of Comparative Example 1.

FIG. 6A is a side view showing a rolling conveyance device according to a related art.

FIG. 6B is a cross-sectional view showing adjacent aluminum bars on the rolling conveyance device according to the related art.

FIG. 6C is an enlarged cross-sectional view showing contour lines of the adjacent bars at a contact point thereof on the rolling conveyance device.

FIGS. 7A and 7B show damage and its periphery, the damage being formed on a surface of an aluminum bar, wherein FIG. 7A is a plane view thereof and FIG. 7B is a cross-sectional view thereof.

EMBODIMENT FOR CARRYING OUT THE INVENTION

In the following paragraphs, some embodiments of the present invention will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.

An aluminum bar to be produced using a production method according to an embodiment of the present invention is used as a material to be forged (which is referred to as “forging blank” in this disclosure). The material of the aluminum bar of this embodiment is not especially limited as long as it is made of pure aluminum or aluminum alloy. Among other things, an aluminum alloy of hypereutectic Si (Si content rate of 12 to 18 wt %) which is an especially hard-to-cut material, or an aluminum alloy which is low in so-called “0-material” (i.e., annealed aluminum material) hardness in which damage easily occurs, e.g., 1000 series, 3000 series, 5000 series, 6000 series JIS alloy number aluminum alloys, can be suitably used.

The production method of this embodiment is equipped with a consistent production line for producing a continuously cast bar. The production line includes a casting step for obtaining a continuously cast bar, a cutting step for cutting the continuously cast bar, a heat treatment step (homogenization treatment step) for subjecting the cut continuously cast bar to a heat treatment, a pre-straightening step (first straightening step) for straightening the heat-treated continuously cast bar, a peeling step for cutting and removing the surface of the pre-straightened continuously cast bar, a post-straightening step (second straightening step) for correcting the bend of the continuously cast bar in which the surface is in contact, a visual inspection step for inspecting the post-straightened continuously cast bar, and a packing step for packing the inspected continuously cast bar.

The peeling step in this embodiment is performed for the purpose of removing the inverse segregation layer on the surface. The peeling step is a process to cut about 1 mm to 3 mm of the surface of the bar, and it can be performed using a peeling device, a lathe device, etc. In this embodiment, it is preferable that the surface roughness (Ra) of the aluminum bar is adjusted to 5 μm or less with this peeling step.

In this embodiment, the post-straightening step is performed after the peeling step, but the post-straightening step has a specific configuration.

FIG. 1A and FIG. 1B show a roll straightening machine 5 used in the post-straightening step. As shown in both the figures, the roll straightening machine 5 is equipped with a pair of upper and lower straightening rolls (which is also called “correction rolls” (pressure rollers) 51 and 52 capable of sandwiching an aluminum bar W. The pair of straightening rolls 51 and 52 is arranged so as to intersect in a planar view (see FIG. 1A).

The upper straightening roll (roller) 51 has a drum-shape in which the circumferential surface curves in a concave shape. The lower straightening roll (roller) 52 has a drum-shape in which the circumferential surface bends in a convex shape.

To process an aluminum bar W using this roll straightening machine 5, at least one of the pair of straightening rolls 51 and 52 is rotated by a driving mechanism (not illustrated), and by introducing the aluminum bar W between the pair of straightening rolls 51 and 52, the aluminum bar W is carried in the conveyance direction (left direction in FIG. 1A) while rotating. At the time of the conveyance, the surface pressing process is performed since the surface of the aluminum bar W is pressed by the pair of straightening rolls 51 and 52, and at the same time, the bend is corrected to improve the straightness.

The distance between the pair of straightening rolls 51 and 52 (roll distance) is configured to be adjustable, and is adjusted according to the outer diameter dimension of the aluminum bar W, etc.

Further, in a planar view (see FIG. 1A), the angle (roll angle) Rβ of the rotational axis of the upper straightening roll 51 and the angle (roll angle) Rα of the rotational axis of the lower roll 52 with respect to the conveyance axis of the aluminum bar W are configured to be adjustable. With this adjustment, the contact distance of each of the straightening rolls 51 and 52 and the aluminum bar W can be adjusted. Furthermore, by adjusting the contact distance in this way, the surface pressing process can be performed efficiently even when the cross-section of the aluminum bar W is not a perfect circle.

In this embodiment, the rolling force (rolling load) of the straightening rolls 51 and 52 against the aluminum bar W can be adjusted by the roll distance (roll position) and the roll angles Rα and Rβ. Furthermore, the pressing force (processing degree) of the straightening rolls 51 and 52 to the aluminum bar W is based on the aforementioned rolling force (rolling load) and the rotation number of the straightening rolls 51 and 52, and therefore, the terms “pressing force” and “rolling force” are not used as a synonym.

The inventors have found the fact or configuration that, in the post-straightening step in the aforementioned series of production line, by setting the pressing force (processing degree) of the straightening rolls 51 and 52 within a specific range, the bend can be corrected and the surface of the aluminum bar W can be adjusted to a good state, which in turn can prevent occurrence of detrimental damage. Hereinafter, the specific configuration will be explained.

FIG. 2 is a graph showing the relationship between the straightness (degree of correction), the surface profile and the deformation amount of the outer diameter/length (deformation amount of the outer diameter/length) of the aluminum bar W and the straightening rolling force (rolling load) in the post-straightening step. In this graph, the vertical axis shows the straightness, the surface profile and the deformation amount of the outer diameter/length, and the values become better toward the bottom side. The horizontal axis shows the straightening rolling force and becomes larger toward the right side. Furthermore, for the curved lines in this graph, the alternate long and short dash line shows the straightness, the solid line shows the surface profile, and the short dashed line shows the deformation amount of the outer diameter/length. Further, the value of the rolling force in this graph is shown as a ratio when the rolling force at a later-described roundness saturation point is “1”.

Focusing on the straightness (degree of correction) as shown by the alternate long and short dashed line in FIG. 2, the numerical value of the straightness gradually decreases and the straightness gradually improves in a section where the rolling force is from “0” to “1”. However, in a section in which the rolling force is more than “1” (“1” to “5”), the straightness does not change and is constant although the rolling force is increasing. In this embodiment, a boundary point where the straightness transfers from a section in which the straightness decreases (changes) to a section in which the straightness is constant (does not change) will be referred to as “roundness saturation point (straightening degree saturation point)”. Here, a section after the roundness saturation point (roundness saturation range) is a section in which the roundness shows little change even when the rolling force increases, for example, a section in which the deformation amount of the roundness is 0.2 mm or less per meter (mm/m or less).

Next, focusing on the deformation amount of the outer diameter/length as shown by the short dashed line in FIG. 2, the deformation amount of the outer diameter/length gradually increases along with the increase in the rolling force. When the rolling force is set in a section in which the rolling force is from “4” to “5” (overstraightening range), the aluminum bar becomes in an overstraightened state, which causes occurrence of a detrimental transfer mark on the aluminum bar W by the straightening rolls 51 and 52, a detrimental deformation, such as elongation of the bar W due to the reduction of the outer diameter thereof. In other words, when the rolling force is “4” or less, occurrence of a detrimental transfer mark, a deformation, etc., can be controlled.

Under these conditions, in a typical straightening step, it is common to adjust the rolling force by the straightening rolls to around “1” for the purpose of prevention of overstraightening, alleviation of labor, improvement of work productivity, reduction of load on a workpiece, etc.

However, the inventors were not satisfied with the conditions, and repeated detailed experiments and research. As a result, the inventors found that, with an innovative configuration that the rolling force of the straightening rolls 51 and 52 is set to be significantly larger than around “1”, the surface of the aluminum bar W can be pressed and processed to have a good surface profile (good state) and occurrence of damage can be effectively prevented while preventing occurrence of a roll transfer mark and a deformation of the aluminum bar W.

In this embodiment, the surface profile is defined by a load curve parameter tan(Pθmin) which is obtained based on the load curve of the surface of the aluminum bar W after the straightening. The details will be explained later. In this embodiment, in the aluminum bar W in which the surface profile is adjusted so as to fall within a predetermined range, the state of the surface becomes good and occurrence of damage can be prevented.

In the graph of FIG. 2, focusing on the surface profile shown by the solid line, in a section in which the rolling force is from “0” to “around 1.8”, the surface profile gradually decreases, i.e., improves. However, in a section in which the rolling force is larger than “around 1.8”, the surface profile does not change and is constant although the rolling force is increasing. In this embodiment, the boundary point where the surface profile transfers from a section in which the surface profile decreases to a section in which the surface profile is constant as the rolling force increases will be referred to as the “surface profile saturation point”. Further, according to the graph in FIG. 2, at the time when the rolling force is “1.5”, the surface profile is at the upper limit in a suitable range, and when the rolling force is “1.5” or more, the surface profile is in a good range (section).

According to the aforementioned results, when the rolling force is “1.5” or more, a good surface profile can be obtained and occurrence of damage can be effectively prevented. Further, when the rolling force is “4.0” or less, a detrimental transfer mark, a deformation, etc., by the straightening rolls can be suppressed. Therefore, in this embodiment, in the straightening step, the rolling force of the straightening rolls needs to be set to 1.5×“1” to 4.0×“1”, with reference to the rolling force “1” at the straightness saturation point (straightening degree saturation point).

Here, the section in which the rolling force is 1.5×“1” to 4.0×“1” is also referred to as a semi-overstraightened range, and as explaining repeatedly, an aluminum bar having a good surface state can be obtained by performing a straightening process (surface pressing process) with a rolling force in such a range.

Specifically, as will be explained in the following Examples, in the case of a 4000 series aluminum alloy bar having a diameter of φ25 mm, the roundness saturation point becomes “1” when the rolling force of the straightening rolls is 0.5 ton (0.5×10³×9.80 N), it becomes a semi-overstraightened range in a section where the rolling force is 0.75 ton (0.75×10³×9.80 N) to 2.0 ton (2.0×10³×9.80 N). When the rolling force is set in this range, an aluminum bar having a good surface profile can be obtained. Further, in a section where the rolling force exceeds 2.0 ton (2.0×10³×9.80 N), it becomes an overstraightening range. When the rolling force is set within this range, a detrimental deformation may occur due to occurrence of stretching in the aluminum bar or reduction of the diameter of the bar, and/or a detrimental roll transfer mark may occur on the aluminum bar.

In this embodiment, the surface profile is determined by the pressing force (processing degree) applied to the surface of the aluminum bar W. As explained above, the pressing force is affected not only by the rolling force (rolling load and roller angle) of the straightening rolls, but also by the number of rotations per unit time of the straightening rolls. However, since the pressing force and the rolling force are correlated, a relational expression of the pressing force and the surface profile can be derived based on the relational expression of the rolling force and the surface profile.

That is, when the pressing force by the straightening rolls at the straightness saturation point is “Fc”, in the straightening step, by setting the pressing force by the straightening rolls within a range of 1.5×“Fc” to 4.0×“Fc”, an aluminum bar having a good surface profile can be obtained, which enables to prevent occurrence of damage, and also enables to assuredly prevent occurrence of inconvenience such as a detrimental roll transfer mark, a deformation of the outer diameter, etc.

For example, as shown by the symbols in parentheses in FIG. 2, when the pressing force is set to “Fb” and “Fa”, which are, respectively, two times and four times the straightness saturation point “Fc”, an aluminum bar having a good surface profile can be obtained. When the pressing force is set to “Fd” which is five times the straightness saturation point “Fc”, it becomes difficult to obtain an aluminum bar having a good surface profile.

As a specific example, for a cylinder shaped aluminum bar having a diameter (outer diameter) of φ23 mm, when the roll angles Rα and Rβ of the straightening rolls 51 and 52 are set to 13° to 15°, by adjusting the roll distance in accordance with the aluminum bar and setting the roll rotational number to 600 rpm to 1,200 rpm, the pressing force can be set so as to fall within the straightness saturation range (correction degree saturation range) which is a section beyond the straightness saturation point (correction degree saturation point) Fc. Further, when the pressing force is increased by narrowing the roll distance and/or reducing both the roll angles Rα and Rβ, it can be adjusted to the semi-overstraightened range (suitable range), which enables to obtain an aluminum bar having a good surface profile (1.5×Fc or more).

As described above, in this embodiment, by setting the pressing force within the aforementioned specific range to perform the post-correction step, even when surface treated aluminum bars W are rolled and carried by a rolling conveyance device as shown in FIG. 6A, damage can be prevented from being occurred on the surface, and an inconvenience such as transferring of damage between aluminum bars W can be assuredly prevented. For example, in an aluminum bar W obtained by this embodiment, the number of detrimental damage per 1 m length becomes 0.1 pieces (pieces/m).

In this embodiment, the aluminum bar W will be used as a forging blank through an inspection step and a binding and packing step after performing a post-straightening step. For example, after subjecting the aluminum bar as a forging blank to a cutting step, a preliminary heating step and a lubricant treatment step, the forging blank is introduced into a mold in a forging device in the forging step and molded to produce a predetermined forging blank.

A forging blank obtained as mentioned above can prevent occurrence of damage on the surface, and also can prevent occurrence of a plastically deformed part in which a convex shaped damage is crushed into a layer shape so as to be covering, which in turn can prevent occurrence of a lap defect such as a minute crack. Therefore, a high quality forged product can be assuredly obtained.

FIG. 3 is a graph showing a load curve for explaining a surface profile according to this embodiment.

This curve line in this graph is a load curve (bearing curve) on a surface of an aluminum bar after straightening (after pressing), and is stipulated in JIS B0671. In this graph, the vertical axis shows a cutting level (%) to a contour curve of a surface shape, and the horizontal axis shows a load length rate (%) of the contour curve. Specifically, the horizontal axis is a ratio of a load length of a contour curve element to an evaluation length (entire length of the load length) of each cutting level. Further, the cutting level and the load length may be denoted with a unit of length such as μm, etc.

In this embodiment, among two points on the load curve, two points (for example, “A1, A1”, “A2, A2”, etc.) in which the interval of the load length (difference in the load length) is 60% of the length of the entire length (100%) of the evaluation load length (evaluation length) are referred to as “pair of measurement points”. The minimum value of the slope (tangent of the straight line and the horizontal axis (X axis)) of the straight line (line segment A1-A1, line segment A2-A2, etc.) passing through the pair of measurement points is defined as “surface profile (load curve parameter)”. In other words, the angle value of a secant (line segment A1-A1, line segment A2-A2, etc.) passing through two points (“A1, A1”, “A2, A2”, etc.) on the load curve in which the interval of the load length is 60% of the entire length (100%) of the load length is referred to as “P θ”. And among the slopes of secants “tan(P θ)”, the slope of the secant having the least steep slope “tan(Pθmin)” is defined as “surface profile (load curve parameter)”.

Specifically, in the graph of FIG. 3, among the straight lines (secants) passing through the pair of measurement points, the inclination angle “Pθmin” of the line segment A1-A1 is the smallest, and the slope of the line segment A1-A1 “tan(Pθmin)” becomes the surface profile (load curve parameter) of the aluminum bar.

In this embodiment, when the load curve parameter tan(Pθmin) is 0.5 or less, the surface state of the surface profile becomes good and occurrence of damage can be prevented. Further, when the load curve parameter tan(Pθmin) exceeds 0.5, the surface state of the surface profile becomes insufficient, and damage may occur.

Therefore, in this embodiment, in the aforementioned post-straightening step, by setting the pressing force by the straightening rolls to a range of 1.5 Fc to 4.0 Fc as described, an aluminum bar having a good surface profile in which the load curve parameter tan(Pθmin) is 0.5 or less can be produced.

In this embodiment, a continuously cast bar is used as an aluminum bar, but in the present invention, bars other than continuously cast bars can be used. For example, in the present invention, an extruded bar obtained by extruding a cast billet can also be used.

Further, in the aforementioned embodiment, a case in which a pressing step is also used as a straightening step was explained, but it is not limited to that. In the present invention, a surface pressing step can be performed separately from the straightening step (post-straightening step).

EXAMPLES

An Al—Si—Cu—Mg alloy (Si: 11%, Cu: 4.5%, Mg: 0.7%, and the balance being Al and inevitable impurities) was subjected to continuous casting to obtain a cylinder shaped aluminum alloy continuously cast bar having a diameter of 30 mm.

The surface of the aluminum alloy continuously cast bar was removed by a cutting process to prepare a cut (unstraightened) aluminum alloy bar (aluminum bar).

TABLE 1 Surface Surface Pressing State Process Load Curve Effect of Damage Diameter/Length Processing Pressing Pressing Parameter Occurrence Dimensional Change performed Point Force *1 tan(Pθmin) Prevention Forging Defect Straightness Roll Transfer Mark Ex. 1 Yes Fa 4 0.42 ∘ ∘ ∘ ∘ Ex. 2 Yes Fb 2 0.38 ∘ ∘ ∘ ∘ Com. Ex. 1 No — — 0.7 x x Δ ∘ Com. Ex. 2 Yes Fc 1 0.61 Δ Δ ∘ ∘ Com. Ex. 3 Yes Fd 5 0.43 ∘ ∘ ∘ x *1: The pressing force is shown as a ratio when the saturation point of the straightness is 1.

Example 1

The aforementioned cut aluminum alloy bar was subjected to a surface pressing process (straightening process) using a roll straightening machine similar to the machine shown in FIG. 1A and FIG. 1B to obtain an aluminum alloy bar of Example 1. For the conditions of the straightening process, the roll angles Rα and Rβ (see FIG. 1A) were set to 14° (degrees) and 14° (degrees), the rolling load was set to 2.0 ton (2.0×10³×9.80 N), and the roll rotational number was set to 1,200 rpm.

Further in Table 1, the pressing force corresponding to the rolling load is shown as a ratio when the straightness saturation point (straightening degree saturation point) at the rolling load of 0.5 ton (0.5×10³×9.80 N) is “1”. Furthermore, the pressing points “Fa” to “Fd” in Table 1 show that they correspond to the pressing points “Fa” to “Fd” in the graph of FIG. 2, and Example 1 corresponds to the pressing point “Fa” in the graph of FIG. 2.

Further, when the load curve of the surface of the aluminum bar in Example 1 was measured, it was a load curve as shown in FIG. 4. Furthermore, when the abovementioned load curve parameter (surface profile) tan(Pθmin) was determined from the load curve, it was 0.42.

Further, as shown in Table 1, for the aluminum of Example 1, each of the “effect of damage occurrence prevention”, the “forging defect”, the “straightness”, the “outer diameter/length dimensional change/roll transfer mark” was evaluated.

The evaluation of the effect of damage occurrence prevention (degree of damage occurrence) for the aluminum bar of Example 1 was performed based on the number of occurrences of damage per 1 m of length. That is, it was “∘ (Good)” when it was less than 0.10/m, “Δ (somewhat poor)” when it was 0.10/m or more and less than 1.0/m, and “x (poor)” when it was 1.0/m or more.

The evaluation of the straightness of the aluminum bar of Example 1 was performed based on the displacement (mm) of the axial center per 1 m of length. That is, it was “∘(good)” when the displacement was less than 0.7 mm/m, “Δ(somewhat poor)” when it was 0.7 mm/m or more and less than 1.0 mm/m, and “x(poor)” when it was 1.0 mm/m or more.

In the evaluation for the outer diameter•length dimensional change/roll transfer marks for the aluminum bar in Example 1, when the deformation ratio of the length measurement was 0.2% or less, the amount of deformation of the outer diameter was 0.05 mm or less, and there were no spiral shaped unevenness (transfer marks) from the straightening rolls, it was evaluated as “∘(Good)”. Further, when the deformation ratio of the length measurement exceeded 0.2%, the amount of deformation of the outer diameter exceeded 0.05 mm, and there were spiral shaped unevenness (transfer marks) from the straightening rolls, it was evaluated as “x(defective)”.

In the evaluation of the forging defect, the aluminum bar of Example 1 was cut into predetermined lengths to obtain forging blanks, and the evaluation was performed based on the rate of occurrence of forging defects on the forged product (forging blank) obtained by upsetting (forging) the forging blank. That is, it was “∘(Good)” when the rate of occurrence was less than 1%, “Δ(Somewhat poor)” when it was 1% or more and less than 5%, and “x(Poor)” when it was more than 5%.

As shown in Table 1, in the aluminum bar of Example 1, all evaluations were “∘(Good)”.

Example 2

For a cut aluminum bar, the rolling load was set to 1.0 ton (1.0×10³×9.80 N) (the pressing point corresponds to Fb of FIG. 2), and other than that, a surface pressing process (straightening process) was performed under the same pressing process conditions as the aforementioned Example 1 to obtain an aluminum bar of Example 2. The load curve parameter tan(Pθmin) of the aluminum bar was 0.38.

Furthermore, as shown in Table 1, also for the aluminum bar of Example 2, all evaluations were good after performing the same evaluations as above.

Comparative Example 1

A cut aluminum bar was used as it was as the aluminum bar of Comparative Example 1 without performing a straightening process (surface pressing process). When the load curve of the aluminum bar was measured, the load curve was as shown in FIG. 5. Furthermore, when the abovementioned load curve parameter (surface profile) tan(Pθmin) was determined from the load curve, it was 0.70.

Further, as shown in Table 1, the same evaluations as described above were performed for Comparative Example 2, but good evaluations could not obtained for the evaluations of the effect of damage occurrence prevention, the forging defect, and the straightness.

Comparative Example 2

For a cut aluminum bar, the rolling load was set to 0.5 ton (0.5×10³×9.80 N) (the pressing point corresponds to Fc of FIG. 2), and other than that, a straightening process was performed under similar pressing process conditions as the aforementioned Example 1 to obtain the aluminum bar of Comparative Example 2. The load curve parameter tan(Pθmin) of the aluminum bar was 0.61.

Further, as shown in Table 1, the same evaluations as described above were performed for the aluminum bar of Comparative Example 2, but good evaluations could not be obtained for the evaluations of the effect of damage occurrence prevention and the forging defect.

Comparative Example 3

For a cut aluminum bar, the roll angles Rα and Rβ were set to 15° (degrees) and 13° (degrees) and the rolling load was set to 2.5 ton (2.5×10³×9.80 N) (the pressing point corresponds to Fd of FIG. 2), and other than that, a straightening process was performed under similar pressing process conditions as the aforementioned Example 1 to obtain the aluminum bar of Comparative Example 3. The load curve parameter tan(Pθmin) of the aluminum bar was 0.43.

Further, as shown in Table 1, the same evaluations as described above were performed for the aluminum bar of Comparative Example 3, but good evaluations could not be obtained for the evaluations of the outer diameter/length dimensional deformation/roll transfer marks.

<Comprehensive Evaluation>

When Example 1 and Comparative Example 1 were compared, in Comparative Example 1 in which a roll straightening (straightening process) was not performed, the load curve parameter tan(Pθmin) exceeded 0.50, and sufficient effect of damage occurrence prevention, etc., could not be obtained. On the other hand, in Example 1 in which the load curve parameter tan (Pθmin) was 0.50 or less, sufficient effect of damage occurrence prevention, etc., was obtained.

In Comparative Example 2, roll straightening was performed, but since the pressing force was less than the predetermined value (1.5×Fc) and was small, the load curve parameter tan(Pθmin) exceeded 0.50, and sufficient effect of damage occurrence prevention, etc., could not be obtained.

In Comparative Example 3, since the pressing force exceeded the predetermined value (4.0×Fc) and was large, overstraightening occurred, making the outer diameter/length dimensional deformation amount large, and occurrence of spiral shaped detrimental unevenness (transfer marks) from the rolls was recognized.

When Examples and Comparative Examples were compared, when the pressing force was 1.5×Fc or more, the load curve parameter tan(Pθmin) was 0.50 or less, and good evaluations were obtained for the effect of damage occurrence prevention, forging defect, and straightness. When the pressing force was 4.0×Fc or less, overstraightening did not occur, and good evaluations were obtained for the outer diameter/length dimensional deformation/roll transfer marks.

The terms and descriptions used herein are used only for explanatory purposes and the present invention is not limited to them. The present invention allows various design-changes falling within the claimed scope of the present invention unless it deviates from the spirits of the invention.

INDUSTRIAL APPLICABILITY

The method of producing an aluminum bar of the present invention can be used, for example, when producing an aluminum bar which is used as a forging blank.

It should be understood that the terms and expressions used herein are used for explanation and have no intention to be used to construe in a limited manner, do not eliminate any equivalents of features shown and mentioned herein, and allow various modifications falling within the claimed scope of the present invention.

While the present invention may be embodied in many different forms, a number of illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein.

While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. 

1. A production method of an aluminum bar, comprising: a surface pressing step of pressing a surface of an aluminum bar with pressure rollers, wherein a pressing force of the pressure rollers in the surface processing step is set within a range of 1.5 Fc to 4.0 Fc, where, in a relationship between a pressing force of the pressure rollers to the aluminum bar and a straightness of the aluminum bar, when a boundary point at which a section where the straightness of the aluminum bar improves as the pressing force of the pressure rollers increases shifts to a section where the straightness does not change as the pressing force of the pressure rollers increases is a straightness saturation point, and the pressing force of the pressure rollers at the straightness saturation point is “Fc”.
 2. The production method of an aluminum bar as recited in claim 1, wherein a pair of straightening rolls are used as the pressure rollers, and wherein a straightening step for straightening an aluminum bar by passing the aluminum bar between the pair of rotating straightening rolls is also used as the surface pressing step.
 3. The production method of an aluminum bar as recited in claim 1, further comprising a peeling step of cutting and removing an outer peripheral surface of the aluminum bar before performing the surface pressing step.
 4. The production method of an aluminum bar as recited in claim 1, wherein the aluminum bar is an aluminum member to be used as a forging blank.
 5. An aluminum bar produced by the production method as recited in claim 1, wherein, among two points set on a load curve showing a relationship between a cutting level and a load length for a contour curve on a surface of the aluminum bar, when two points in which an interval of the load length becomes 60% of the entire length of the load length are a pair of measuring points, a minimum value of a slope of a straight line passing the pair of measuring points is 0.5 or less. 